1. Field of the Invention
The invention relates to devices for measuring signals in the field of wideband phenomena.
More precisely, the present invention relates to a device for the processing of signals coming from nuclear electromagnetic impulse sensors (EMI), lightning sensors or electromagnetic compatibility (EMC) sensors. Sensors such as these may consist of wideband sensors of electrical or magnetic fields, currents or surface charges, having a frequency response ranging from about 10-100 kHz to more than one GHz.
2. Description of the Prior Art
In a known way, these sensors may be either passive sensors or active sensors.
Passive sensors use sensing elements connected to a low-impedance load with a value of 50 .OMEGA. for example.
The connection between the sensor and the load is usually made by a cable with the same impedance. The working principle of passive sensors is described, for example, in the article by Carl Baum, Edward Breen, Joseph Gilles, John O'Neill, Gary Sower, "Sensors for Electromagnetic Pulse Measurements both Inside and Away from Nuclear Source Regions", IEEE Transactions on Antennas and Propagation, Vol. AP-26, No. 1, January 1978.
Passive sensors such as these have a derivative response that requires processing to obtain the real shape of the signal to be measured. The processing consists in integrating the signal coming from the sensor, for example by means of an RC cell, and in amplifying the integrated signal by means of an amplifier with an impedance that is higher than the equivalent impedance of the integrator.
The main advantage of passive sensors is that they let through high frequencies which may go up to 10 GHz. Furthermore, passive sensors are simple to make. However, the drawback of such sensors is that they have reduced sensitivity.
Active sensors, by contrast, have an electrical field and magnetic field measuring sensitivity that is respectively up to 100 times and 3000 times greater than the sensitivity of passive sensors.
Active sensors of this type are described, for example, in Gregoire Eumurian, "Computer-assisted Control of EMP Measurement on Major Systems", Proceedings of the 6th Symposium on Electromagnetic Compatibility, Zurich, 1985.
Signals coming from an electrical field measuring active sensor are processed by a very high impedance (&gt;1 M.OMEGA.) amplifier and, and for a magnetic field measuring active sensor, this processing is done by a high impedance coil with magnetic core.
Active sensors are suited to applications of up to 200-300 MHz but, for applications beyond these values, it becomes difficult to make their internal electronic circuitry.
Besides, this electronic circuitry results in bulkier sensors. This is contradictory to the rise in frequency and, hence, to the reduction in the wavelength.